This study was to investigate the levels and needs of perceived professional competency of junior high school and elementary school teachers of students with intellectual disability, and further probed into the differences in the levels and needs of those teachers with different background variables. A questionnaire survey was conducted on the teachers of students with intellectual disability in junior high schools and elementary schools of Taipei City, New Taipei City, Taoyuan County, Hsinchu County, Hsinchu City, Miaoli County, Taichung City, and Changhua County in the academic year of 2009. The research tool was the questionnaire designed by this study. A total of 1531 questionnaires were distributed and 990 effective samples were retrieved, with a valid return rate of 64.7%.The results found that the perceived professional competencies of teachers of students with intellectual disability, in the order of its level, are "curriculum planning and design", "teaching ability", and "basic special education competency"; the competencies in the order of its needs are "curriculum planning and design", "basic special education competency", and "use of assistive technology". The differences in the levels and needs of perceived professional competency of teachers of students with intellectual disability vary significantly due to the variables of years of teaching, highest education, and educational background in special education. Lastly, this study suggested that the educational authorities should strengthen the compilation of the curriculum materials, using assistive technology, as well as improve the communication and cooperation between the regular teachers and related professionals.